How accurate are early dating/reassurance scans?

[isl7]

So I’m very confused! My LMP was 23rd July so I had dated myself at 8 weeks 6 days. Although my periods have been irregular since coming off the pill in April (anything from 15-35 days).

Went for a private reassurance scan today and they dated me at only 5 weeks 6 days! Not only was this pretty disappointing to be put back 3 weeks, it’s also pretty confusing. We only did the deed 6, 10 and 19 August. Nothing since! (Another story!...) So surely if we conceived 19 August I should be further along than 5 weeks 6 days? How accurate are these early scans?

I’m also really not sure what to do about my nhs 12 week scan. I have heard not to tell them about private ones in case they refuse your 12 week one, but I’m worried it will be too early if I don’t tell them and then they may not re scan me?! Im also a really bad liar :D

I forgot to add they told me today I have a retroverted uterus - not sure if that’s relevant?

Mine seemed accurate to me, but I suppose everything is different.
They don't just check size but development. I'd say a scan would be more realistic to your missed period but I'm not sure how it could be so off.
When did you get you BFP?
I knew when I ovulated and estimated from then I'd be 7 weeks 1 days when I had my early scan and they said i was at the early stage of 7 weeks. So it was right for me.
If the midwife is happy to go off your LMP I'd just go with it.

Yes I would have thought a scan would be more realistic but it just doesn’t make sense with the dates we did the deed (I don’t know when I ovulated). I got my BFP 1st September

Did they see a heartbeat OP?

I have to be honest and say that when this happened to me, it wasn’t good news. I knew I should be around 8 weeks and I measured at around 5 1/2. I really hope this isn’t the case for you. Best of luck.

Was the scan internal or external? Early on that can really make a difference to accuracy.

Thanks for the comments guys and your honesty @PrimeraVez . We did see the heartbeat though yes and it was internal

Unfortunately my experience of this was the same as @PrimeraVez. If you can, I would try to get referred to an Early Pregnancy Unit because either way they will be able to offer further scans, support and/or reassurance. Fingers crossed that all is well for you and good luck with everything.

Mine were accurate to within a day or 2 of when I thought conception was. I second what grouchymamabear says re trying to get an EPU referral

@PrimeraVez and @grouchymamabear did you still see a heartbeat? I wouldn’t have thought I would if that was the case?

Yes, we did see a heartbeat, but when I went back 2 weeks later it had stopped. I really hope you get some clarity soon and I have my fingers crossed for you that this is just one of those weird things - there are certainly plenty of stories out there of women in similar situations who had a happy ending.

If you conceived August 19 then those dates are fine - you are pretty much six weeks. Remember that sperm can live inside you for a few days too. When you conceive you are already classed as two weeks pregnant.

Last period only works for dating if you have somewhat reliable cycles. My LMP would put me a week ahead of what I am, but I have long cycles and know exactly when I ovulated (and have measured the whole way through exactly according to my own dates, not LMP)

Thanks @PrimeraVez and sorry that must have been awful. I saw the heartbeat today though so probably not much point going to th EPU.

Thanks for the reassurance @Celebelly I just worked it out and guess if the sperm stayed in the max 5 days, I would be 6 weeks 1 day today so I suppose only a few days out. Fingers crossed...

Dating is less definite at that early stage as the baby is much smaller and harder to measure accurately - that’s why the NHS don’t date you by scan until 12 weeks.

Sperm can survive several days before conception so if you conceived a few days after the 19th that would put you roughly around six weeks.

I would go for the NHS scan as planned and see how things are going as they can rebook you for later if it’s too early for dating/NT measurements.

I was told this many times that all scans before 12 weeks are the most accurate. They said the reason is all babies grow at same rate at this stage but after that they grow at different rates (hence bigger babies etc).
When I went for early scan I was 9+3 based on LMP but they put me at 6+5.
I think it must have been accurate though because I gave birth 44 weeks and 5 days after my LMP! Which obviously couldn't be correct- their calculations dated it at 42 weeks (I got induced then as she still wasn't ready to come!!)

Thanks everyone. I think I’ll wait for the nhs scan then and see what happens

Our early scan was an u known date (mini pill baby) but dated 25th Feb then we had another private a few weeks later at 23rd Feb and our actual 12 weeks was 21st Feb.

I think they're accurate within certain dates. Our family tend to have big babies which could be why.

Hope it all works out.